From: Chris Wilson Date: Fri, 12 Jul 2019 08:03:14 +0000 (+0100) Subject: dma-buf: Relax the write-seqlock for reallocating the shared fence list X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=30fe7b07f6cb7f391181eb9d2ea2687cd9bcf395;p=openwrt%2Fstaging%2Fblogic.git dma-buf: Relax the write-seqlock for reallocating the shared fence list As the set of shared fences is not being changed during reallocation of the reservation list, we can skip updating the write_seqlock. Signed-off-by: Chris Wilson Cc: Daniel Vetter Cc: Christian König Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20190712080314.21018-2-chris@chris-wilson.co.uk --- diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index 80ecc1283d15..c71b85c8c159 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -157,15 +157,15 @@ int reservation_object_reserve_shared(struct reservation_object *obj, (ksize(new) - offsetof(typeof(*new), shared)) / sizeof(*new->shared); - preempt_disable(); - write_seqcount_begin(&obj->seq); /* - * RCU_INIT_POINTER can be used here, - * seqcount provides the necessary barriers + * We are not changing the effective set of fences here so can + * merely update the pointer to the new array; both existing + * readers and new readers will see exactly the same set of + * active (unsignaled) shared fences. Individual fences and the + * old array are protected by RCU and so will not vanish under + * the gaze of the rcu_read_lock() readers. */ - RCU_INIT_POINTER(obj->fence, new); - write_seqcount_end(&obj->seq); - preempt_enable(); + rcu_assign_pointer(obj->fence, new); if (!old) return 0;